False, but only just. There are only two specific instances that we know of when the great man laughed. One was when a friend to whom he had lent a volume of Euclid’s Elements asked what the point of it was, ‘upon which Sir Isaac was very merry.’ (The point being that if you have to ask what the point of Euclid is, you have already missed it.) So far, so moderately funny. The second time Newton laughed was during a conversation about his theory that comets inevitably crash into the stars around which they orbit. Newton noted that this applied not just to other stars but to the Sun as well and laughed while remarking to his interlocutor John Conduitt ‘that concerns us more.’